CHAPTER 12 Highlights 269
Key Concepts
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How Did Life Begin?
The Earth formed about 4.5 billion years ago according to
evidence obtained by radiometric dating.
The primordial soup model and the bubble model propose
explanations of the origin of the chemicals of life.
Scientists think RNA formed before DNA or proteins
formed.
Scientists think that the first cells may have developed from
microspheres.
The development of heredity made it possible for organisms
to pass traits to subsequent generations.Complex Organisms Developed
Prokaryotes are the oldest organisms and are divided into
two groups, archaebacteria and eubacteria.
Prokaryotes likely gave rise to eukaryotes through the
process of endosymbiosis.
Mitochondria and chloroplasts are thought to have evolved
through endosymbiosis.
Multicellularity arose many times and resulted in many
different groups of multicellular organisms.
Extinctions influenced the evolution of the species alive
today.Life Invaded the Land
Ancient cyanobacteria produced oxygen, some of which
became ozone. Ozone enabled organisms to live on land.
Plants and fungi formed mycorrhizae and were the first
multicellular organisms to live on land.
Arthropods were the first animals to leave the ocean.
The first vertebrates to invade dry land were amphibians.
The extinction of many reptile species enabled birds and
mammals to become the dominant vertebrates on land.
The movement of the continents on the surface of the
Earth has contributed to the geographic distribution of
some species.3
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Key Terms
Section 1
radiometric dating (252)
radioisotope (252)
half-life (252)
microsphere (256)Section 2
fossil (258)
cyanobacteria (258)
eubacteria (258)
archaebacteria(258)
endosymbiosis (259)
protist (261)
extinction (263)
mass extinction (263)Section 3
mycorrhizae (265)
mutualism (265)
arthropod (266)
vertebrate(267)
continental drift (268)